We plan to continue our studies of oxygen transfer and carbon dioxide elimination in the placenta and lungs. We will experimentally study the importance of the various factors affecting respiratory gas exchange in an isolated cotyledon of the sheep placenta perfused in situ. We will simulate the exchange reaction kinetics and diffusion processes using a mathematical model. We will explore the effect of maternal vascular pressure in the placenta on the fetal resistance to blood flow in humans and animals. We will examine the effect of labor contractions in reducing maternal placental blood flow and hence oxygen delivery to the fetus. We will examine pressure-volume and pressure- flow characteristics of uterine and umbilical vessel segments. And finally, we will simulate gas exchange in the human lung in an effort to find which factors are of particular importance to pulmonary O2 and CO2 exchange in the newborn period. The objective of all these studies is to increase our understanding of basic mechanisms and clinical conditions related to fetal oxygenation.